Since you've used this printer for some time it needs a true manual cleaning to remove all crud/build-up. The problem will only get worse and fail all together and only a prthd. replacement will do. For that cost, you're better off buying another printer.
To clean prthd. just shut down during its initial power_ON, pull the AC plug. That way the prthd. carriage can move back and forth by hand. Using a clean shop paper towels(strong) or T-shirts make swatches, moisten(water) and wipe portion of prthd. face. Repeat until clean or appears suitable. Clean also the "parking area/station of its build-up. I don't recommend Q-tips it may leave fibers behind causing issues of its own. Once all done, return Ac cord, redo some cleaning cycles and then test output. If all is OK, it'll run good. If not and problem remains, you have a possible bad prthd. period, it needs replacement. You may have to remove the outer cover to better access the prthd. carriage and parking area. All this cab be done, if you're capable, otherwise think replacement. Buy another i860 used/new via eBay or Craigslist or another Canon printer in order to use any extra ink carts left or move on to entirely new model.
Service manual: http://printer1.blogspot.com/2009/01/canon-i860-i865-service-manual.html (if needed or good reading)
tada -----Willy 